Typical building fire alarm systems include a number of fire detectors positioned throughout a building. Signals from those detectors are monitored by a system controller, which, upon sensing an alarm condition, sounds audible alarms throughout the building. Flashing light strobes may also be positioned throughout the building to provide a visual alarm indication. A number of notification appliances comprising audible alarms and strobes, the audible alarms and strobes being generally referred to as notification devices, are typically connected across common power lines on a notification circuit.
A first polarity DC voltage may be applied across the notification circuit in a supervisory mode of operation. In this supervisory mode, rectifiers at the notification appliances are reverse biased so that the alarms are not energized, but current flows through the power lines at the notification circuit to an end-of-line resistor and back, allowing the condition of those lines to be monitored. Because notification circuits are supervised using an end-of-line resistor, the wires of the circuit must be a single continuous run with no branches and an end-of-line resistor across the wires at the end farthest from the system controller. With an alarm condition, the polarity of the voltage applied across the power lines is reversed to energize all notification appliances on the notification circuit.
U.S. Pat. No. 5,559,492 issued to Stewart et al. (hereinafter the ""492 Stewart patent) operates according to the system described above. The ""492 Stewart patent further discloses that the visual alarms, or strobes, may be synchronized to fire simultaneously resulting from power interruptions, also referred to as synchronization pulses, in the power lines. Additional timing lines for synchronizing the strobes are not required because the synchronizing signals are applied through the existing common power lines.
Other alarm systems have controlled the function of the audible and visual alarms by interrupting the power signal to the alarms in a predetermined pattern as control signals over the common power lines or by communicating during the synchronization interruption of power. The audible and visual alarms operate their respective loads responsive to the control signal received.
Prior art systems have not provided for control signals to be issued from the system controller to the notification appliances during the term of the supervisory mode. As such, prior art systems do not provide for communication between the notification appliances and the system controller during supervisory mode other than passive communication, such as monitoring the common power lines for a short circuit or other fault.
The invention disclosed below provides detailed communication between the system controller and notification appliances during a supervisory or standby mode of operation. This is accomplished by providing notification appliances which are powered during the standby mode by a pair of communication lines at a first voltage level by a system controller. Communication between the notification appliances and the system controller is provided by sending data pulses along the power lines relative to the first voltage level. In an active mode of operation, the first voltage level is raised to a second voltage level providing the power so that the appliances can be commanded on. Communication in the active mode is accomplished by reducing the second voltage level to about the first voltage level and sending data pulses along the power lines relative to the first voltage level.
The communications between the controller and the appliances during the supervisory mode allows the notification circuit including the devices to be supervised. Branching of the circuit is allowed because communication is used to supervise the circuit. Any breaks in the notification circuit wires will inhibit communications to one of the devices and can be quickly identified by the system controller.
Preferably, the data pulses form a digital message that comprises a first synchronization signal, a command field, a data field, and a second synchronization signal. Each notification appliance includes an electronic circuit that receives the digital message and responds to the digital message as directed by the command field.
According to one aspect of the invention, the system controller can synchronize respective timers at each notification appliance on a notification appliance circuit with a digital message comprising a Synchronization Poll. The timer of each notification appliance is used to control timed operation in the notification appliance, such as actuation of an audible and/or visual alarm. An electronic circuit at each notification appliance decodes a multi-bit time descriptor of the Synchronization Poll and resets the timer of the notification appliance to the time of the time descriptor. The Synchronization Poll includes a first synchronization signal, a command signal identifying the synchronization poll as the synchronization poll, the multi-bit time descriptor, and a second synchronization signal.
It is desirable to organize the notification appliances including notification devices into groups such that the system controller can efficiently operate the same. Accordingly, the system controller can apply application specific group numbers to a first notification device of a particular notification appliance via a digital message comprising a Notification Appliance First Notification Device Group Assignment Command. Each notification appliance includes an electronic circuit that decodes a multi-bit command identifying the digital message as a Notification First Notification Device Group Assignment Command. The circuit decodes an address field of the digital message assigning the first notification device a first particular group number. More than one group number may be assigned to the first notification device.
The system controller can apply application specific group numbers to a second particular notification device of notification appliances having at least two notification devices via a digital message comprising a Notification Appliance Second Notification Device Group Assignment Command. Each notification appliance includes an electronic circuit that decodes a multi-bit command identifying the digital message as a Notification Second Notification Device Group Assignment Command. The circuit decodes an address field of the digital message assigning the first notification device a first particular group number. More than one group number may be assigned to the second notification device.
According to a further aspect of the present invention, the system controller can solicit general status information from a cluster or set of notification appliances via a digital message comprising a Cluster Service Poll. Each notification appliance includes an electronic circuit that decodes a multi-bit command identifying the digital message as a Cluster Service Poll and a cluster set address field which addresses a cluster of notification appliances, for example, a set of eight notification appliances. The individual notification appliances of a cluster respond to the Cluster Service Poll at a designated response time which may follow a single synchronization pulse or, alternatively, each notification appliance may follow a respective synchronization response signal. The notification appliance responds with a message indicating the status of the notification appliance.
According to other aspects, an alarm system is provided which includes a plurality of notification appliances, a system controller that communicates with the notification appliances in a standby mode of operation, and a notification circuit that powers the notification appliances and carries the communications between the system controller and the notification appliances. The notification appliances include an electronic circuit to respond to the system controller with indications of appliance state. The system controller uses the communications to supervise the notification appliances.